Production of glycerine



Patented July 29, 1952 f"- Shell Development Company,Emeryvilla Califl, L .acorporation'of Delaware 1 j.lfIo .Dra wing. ApplicationjApril d;l951i" .1 "The invention relates t'o'the' production of glycerine, and it'i's particularly directed'to' an improvement in the method by which glycerine is synthesized by hydrolysis of an aqueous solution of the dichlorohydrin isomers 1,2-dichloro-3- hydroxypropane and 1,3- dichloro 2 hydroxypropane. v I

It is'known that glycerine can be synthesized from allyl chloride by a number of methods. In

one such method the allyl chloride is chlorinated additional evaporat ng -'equipment. Accordingly,

' the practice-haswbeen to strike a-balance between to trichloropropane'which is then hydrolyzed,

though with difficulty, to glycerine. A second process involves the hydrolysis of allyl chloride to allyl alcohol, followed by chlorohydrination of the alcohol to various monochlorohydrins which are then hydrolyzed toglycerine. This is'a rela-- tively straight-forward and easy processsince the allylalcoholjis water soluble and can be readily chlorohydrinated in relatively concentrated solution without excessive by-product formation.

' The present invention is concerned with still a third method which involves the chlorohydrination of allyl chloride in aqueous solution to the dichlorohydrin isomers. The latter are then hydrolyzed to glycerine, following which the water present in the solution is evaporated and the remaining glycerine freed of its salt content. This rnethodis considerably more difficult than that which proceeds through allyl alcohol because "of the low water solubility of allyl chloride.

Chlorohyd'rination of such materials has shown that the desired reaction takes place only in the aqueous phase, whereas the reactions occurring in any water insoluble phase present lead to the formation of water-insoluble by-products. Forthis reason the practicehas been to employ rela-' tively dilute solutions in 'order to minimize the amount of allyl chloride not dissolved in the water phase and thereby reduce the occurrence of side reactions. Further, a certain amount of by-product formation takes place in the aqueous phase, and it has been found that such reactions can also be minimized as the dilution is immersed. While both of -these factors favor the .use of increasingly dilute reaction solutions, the presence of additional water becomes a serious drawback when it becomes necessary to recover the glycerine, for all the water present inthe system must then be removed by evaporation. This evaporation procedure is not only expensive but also serves to effectively limit the amount of glycerinewhich can be producedfrom a given plant unit, forv oncea given installation is complete there is" usually no way in which to expand the capacity of the unit without providing chlorohydrin isomers.

the abnormally dilute dichlorohydrin solutions which are theoretically desired from the product 'yield' standpoint and the more concentrated solutions which present a smaller load on the evaporating units.

It is a general object of the present invention to provide an improved method for synthesizing glycerine by hydrolysis of an aqueous solution of A more particular object is to provide a method whereby the amount of 7 water present in'ithe latter solution can be reduced by'inexpensive'means, thereby decreasin the load which is subsequently placed. on the 'glycerine evaporating units. A further object is to provide a method for decreasing said load even when the dilution of the dichlorohydrin solution is increased. Still anotherobject is to provide a method for "removing part 'of the salt formed prior to the final glycerine concentration step. The natureof other objects of the invention will ing description." I I y l e l It islmy discovery that the foregoing objects are attained bydiverting a portion of the aqueous dichlorohydrin solution, as obtained by reaction a of allyl chloride with chlorine, through a heated reaction vessel "wherein the dichlor'ohydrin isomers present in said diverted portion are converted to'epichlorohydrin, distilling off the epichlorohydrin from said vessel and combining it I with the remaining dichlorohydrin solution, and

hydrolyzing the chlorohydrins in the resulting solution to glycerine. 1

v The glycerine solutions heretofore obtained by hydrolysis of the conventional dichlorohydrin solutions contain from about 2.5 to 5% by weight of glycerine tog'ether with from about 6 to 9% salt. However; by'converting a'portion of the 'dichlorohydrinto epichlorohydrin, it is possible V to" provide glycerine solutions which contain as much as 10, to 15% glycerin'e, thereby greatly reducing the loadplaced on the glycerine evap- "oratingunits. Further, since the salt formed on hydrolysis of j the diverted; dichlorohydrins to epichlorohydrin is. not removed with the epichlorohydrin but is discharged as bottoms from the epichlorohydrin distillation unit along with most of the water introduceditherein, the glycerine evaporating unit. is thus'freed ofa considerable portion of thesalt which otherwise would be present therein WhilenQt-definiteIy, understood, "it is .perhapsjifor this reason thatjthe glycerine' prepared by the method of the present be apparent from a consideration of the followalkaline additive.

4. 7 moles of caustic are added for each mole of dichlorohydrin in the solution. If desired, a buffer, as sodium carbonate, can be added to maintain the solution in the desired pH range. As is the case inthe hydrolysis of dichlorohydrin to epichlorohydrin, hydrolysis of the epichlorohydrin and dichlorohydrin to glycerine is effected at elevated temperatures, usually from about 175 to 225 F. Once the hydrolysis of the glycerine precursors is complete, the glycerine-containing solution is fed to evaporating units where the preciable benefit is obtained by diverting lessthan about 20% of the dichlorohydrin solution to the epichlorohydrin unit. In the preferred practice of the invention from about 35 .to 65% of the M aqueous dichlorohydrin solution is passed through the 'epichlorohydrin unit. The dichloro hydrin isomers in the diverted stream portion are converted to epichlorohydrin in known manner by heating thesolution in'the presence of a suitable alkalineadditive. :At least 2 mole equivalents of said additive-as caustic or lime, for example-are added for each mole of dichlorohydrin present, and preferably there isemployed an excess. of from about 2 to- 20% caustic over the amount theoretically required. One mole equivalent of the alkaline additive goes to neutralize the hydrogen chloride which is present in the solution in equimolar amount with the dichlorohydrin isomers, whereas the other mole equivalent of caustic is that required to convert the dichlorohydrinsto epichlorohydrin. As an alternative procedure, the entireaqueous solution emerging from the dichlorohydrin reactor may be treated with alkaline additive in an amount sufficient to bring the solution to neutrality. When this method is employed, correspondingly smaller amounts of alkaline additive need be supplied in the .epichlorohydrin unit as well as in the sub- .sequentglycerine hydrolysis step.

While a number, of procedures can befemployed to. convert the diverted dichlorohydrin portion to epichlorohydrin, good results have been obtained, by passing the diverted-solution, heated to'a temperature of about 150 to 210 F., into the-upper portion of a stripper unit along with the required amount of the caustic or other The contents of the stripper are heated by live steam which i passed upwardlythroughthe unit. The epichlorohydrin is distilled from the stripper and condensed to an aqueous solution whose concentration is deter- ;mined by the amount of steam admitted to the unit. Thus, condensates may be obtained which contain from about to 40% epichlorohydrin in those cases wherev no portion of the condensate is recycled to the stripper as reflux, though with reflux. the concentration of the epichlorohydrin stream may be increased to 90% or more.

Once the epichlorohydrin formed fromthe diverted dichlorohydrin stream has been recovered bystripping or otherwise, it is combined with the undiverted dichlorohydrin solution to form a muchmoreconcentrated solution of the chlorohydrin glycerine precursors than-would otherwise be obtained. This combined solution is then'hy- 'drolyzed to glycerineand the glycerine recovered from the'res'ulting aqueous solution by a practice of known methods. Thus, the chlorohydr'in solution,"if not already neutralized, is brought'to the neutral'point by the addition of a suitable a'lka linejadjditive which preferably is caustic. In addition; at least one mole of caustic is added for each mole f0'f1 epichlorohydrin present, and i two water and glycerine are distilled off, preferably in vacuo. The vsalt present in the solution precipitates out as the evaporation proceeds and is removed by centrifuging or other convenient method. I r

The present invention is illustrated by the following examples:

Example I In-this operation allyl chloride and chlorine are reacted in aqueous medium to produce'a solution containing approximately 4% by Weight dichlorohydrin isomers, 92% water and the balance impurities. In forming this solution allyl chlorideand make-up water are continuously fed to the reactor in the proportion of 25 volumes of water. for each volume of allyl chloride, the

- chlorine being supplied in substantially equimolar .which is continuously withdrawn from the reactor at a temperature of about 100 F., is brought to a pH of about 8 to 9 by addition of caustic and is then fed to a hydrolyzer wherein the temperature of the solution is maintained at about 200 'F. and where additional quantities of caustic are added in the amount theoretically required to effect hydrolysis of .the dichlorohydrin to glycerine. At theend ofv the hydrolysis period (approximately 5 hours) thereis obtained a solution containing about 3% glycerine, 7% salt and Water. 7

In-this operation there is employed thesame dichlorohydrin solution and glycerine hydrolysis treatment as described in the preceding paragraph. Here, however, 50% of the aqueous dichlorohydrin solution (brought to neutrality by addition of caustic) is diverted through an epichlorohydrin unit. This unitcomprises a conventional stripper column, operated without refiuxjintowhich the diverted dichlorohydrin solution, heated to a temperature of about 200 F., is fed'near the top of the column together with a 457% solutionof caustic in about Ste 10% excess over the equimolar amount theoretically required to hydrolyze the dichlorohydrin to epichlorohydrin. Live steam is' introduced near the bottom 1 of the column(bottoms temperature, 215 F.) in

dichlorohydrin solution and the resulting solution of chlorohydrin glycerine precursors is hydrolyzed to glycerine by heating with caustic as described above. The resulting glycerine solution is now found to contain approximately 5.3% glycerine, 8.3% salt and the balance substantially water. From this it will be observed that by diverting a portion of the dichlorohydrin solution through the epichlorohydrin unit, the concentration of the glycerine in the final product solution has been nearly doubled. Further, the quantity of salt present in the glycerine solution has been reduced by approximately one third.

Example II The operations described in this example are conducted under the same conditions as those described in Example I above, except that here the ratio of water to allyl chloride in the dichlorohydrin reactor is increased from 25:1 to 37:1. This change in reaction conditions has the desirable efiect of increasing to 91.5% the conversion of allyl chloride to dichlorohydrin isomers and results in a solution containing approximately 3.5% of said isomers. When this solution is hydrolyzed to glycerine Without diverting any portion thereof through the epichlorohydrin unit, there is obtained a glycerine solution containing approximately 2.6% glycerine. 6.1% salt and the balance water. On the other hand, when 50% or" the dichlorohydrin solution is diverted through an epichlorohydrin stripper, there is obtained a solution containing approximately 4.6% glycerine, 7.2% salt and the balance water. From this it will be observed that even though the dilution of the dichlorohydrin solution is increased to effect higher conversion of the allyl chloride to dichlorohydrin, the resulting glycerine solution contains a higher percentage of glycerine (4.6%) than is obtained when a 25:1 allyl chloride water ratio is used and no portion of the resulting dichlorohydrin solution is fed through the epichlorohydrin unit (3 In a companion operation wherein the portion of the dichlorohydrin solution diverted through the epichlorohydrin unit is raised from 50% to 65%, a glycerine solution is obtained which contains 6% glycerine. 8% salt and the balance water.

The percentages given herein are on a weight basis unless otherwise indicated.

The invention claimed is:

1. In a process wherein an aqueous solution of dichlorohydrin isomers is hydrolyzed to glycerine, the steps comprising diverting from about 20 to 75% of said solution through a unit wherein said dichlorohydrin isomers are converted to epichlorohydrin, combining the epichlorohydrin formed in said unit with the undiverted portion of said dichlorohydrin solution, and hydrolyzing the chlorohydrins present in the resulting solution to glycerine.

2. In a process wherein an aqueous solution of dichlorohydrin isomers is hydrolyzed to glycerine. the steps comprising diverting from about 20 to of said solution through a unit wherein the diverted solution is heated in the presence of at least 2 mole equivalents of an alkaline additive for each mole of dichlorohydrin present to convert said isomers to epichlorohydrin, evaporating the epichlorohydrin from said unit and combining the same with the undiverted portion of said dichlorohydrin solution, and hydrolyzing the epichlorohydrin and dichlorohydrin isomers present in the resulting solution to glycerine.

3. The method of claim 2 wherein the epichlorohydrin-forming unit comprises a stripper column into an upper portion of which the diverted dichlorohydrin solution is introduced and from which substantially all the water present in said solution is discharged as bottoms together with the salt present in the column.

4. The process comprising reacting allyl chloride and chlorine in an aqueous reaction medium to form a solution of dichlorohydrin isomers, diverting from about 20 to 75% of said solution through a unit where, in the presence of heat and an alkaline additive, the dichlorohydrins present in the unit are converted to epichlorohydrin, evaporating the epichlorohydrin from the unit and combining the same with the remaining portion of the dichlorohydrin solution, and hydrolyzing the epichlorohydrin and dichlorohydrin isomers present in the resulting solution, in the presence of heat and an alkaline additive, to glycerine.

5. The method of claim 4 wherein the epichlorohydrin-forming unit comprises a stripper column into an upper portion of which the diverted dichlorohydrin solution is introduced and from which substantially all the water introduced with said solution is discharged as bottoms together with the salt present in the column.

FRANCIS T. TYMSTRA.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,477,113 Essex et a1. Dec. 11, 1923 2,061,377 Groll et a1. Nov. 10, 1936 OTHER REFERENCES Karrer, Organic Chemistry, 3rd English edition, page 301. Published by Elsevier Publishing (20., Inc., New York, 1947. 

1. IN A PROCESS WHEREIN AN AQUEOUS SOLUTION OF DICHLOROHYDRIN ISOMERS IS HYDROLYZED TO GLYCERINE, THE STEPS COMPRISING DIVERTING FROM ABOUT 20 TO 75% OF SAID SOLUTION THROUGH A UNIT WHEREIN SAID DICHLOROHYDRIN ISOMERS ARE CONVERTED TO EPICHLOROHYDRIN, COMBINING THE EPICHLOROHYDRIN FORMED IN SAID UNIT WITH THE UNDIVERTED PORTION OF SAID DICHLOROHYDRIN SOLUTION, AND HYDROLYZING THE CHLOROHYDRINS PRESENT IN THE RESULTING SOLUTION TO GLYCERINE. 